FR2781854A1 - MONOBLOCK PIECE FOR THE PRODUCTION OF A CABLE ANCHORING Jaw, AND METHOD FOR MANUFACTURING SUCH A JIT - Google Patents

Abstract

The invention concerns a single-piece part (20) for producing a cable anchoring jaw, comprising several angular portions (22) arranged about a generally cylindrical duct (5), assembled by clamps (27) adjacent to said duct. Each clamp is located at the bottom of one particular radial slot (25) extending between two portions from the part periphery. Each clamp has towards its own particular slot a surface whereof a part at least is inclined relative to the direction (X) perpendicular to the slot radial plane, such that the clamp radial thickness has a minimum in a specific position along said direction (X), thereby ensuring the position where the clamp (27) will be broken to obtain the jaw wedges from the part portions (22), which enables to better control for clamping the cable strand in the jaw.

Description

MONOBLOCK PIECE FOR THE REALIZATION OF AN ANCHORING BIT OF

  CABLE, AND METHOD FOR MANUFACTURING SUCH A JIT

  The present invention relates to jaws intended to anchor on retaining blocks cables such as cables for prestressing construction works of

deck stays ...

  These jaws usually have a frustoconical shape, and they are provided with an axial channel of generally cylindrical shape receiving the cable strand to be anchored. They cooperate with housings having at least one complementary frustoconical portion, housings hollowed right through in the retaining blocks and traversed by

the cable strands to be anchored.

  The jaws in question are composed of several (usually two, three or four) identical elements - called "keys" below coming from an original part delimited externally by a frustoconical surface and hollowed out by a cylindrical axial channel whose the inner face is advantageously striated. The original part is broken down into keys by sawing according to

  two, three or four (or more) radial half-planes.

  The keys obtained by sawing are subjected to a heat treatment of surface hardening. An annular steel ring is housed in a circular groove, machined on the external frustoconical face of the original part, near its large base, in order

to assemble the keys of the jaw.

  French patent 2,586,076 describes an anchoring jaw made up of keys all coming from the same original part. The sawn timber intended to decompose this part into keys remains voluntarily incomplete so as to let remain small connecting bridges between the adjacent keys along the channel

center of the room.

  -2- This way of making the jaw is well suited to mass production. Even if the cutouts of the keys are not strictly regular and identical, it is ensured that their assembly in the jaw does not cause between the support keys on non-complementary faces which would risk deforming the cylindrical channel in which the strand is gripped. . Manufacturing tolerances and quality controls are therefore less severe than when the sawn timber is complete and the keys stored in bulk between the

cutting and assembly.

  An end view of the one-piece part 1 from which a jaw with three keys 9 is made according to French patent 2,586,076 is shown in FIG. 1. The bridges 7, adjacent to the cylindrical channel 3, are located at the bottom radial slots 6 resulting from sawing carried out from the periphery of the part 1 over its entire length. The bridges are thin (less than 1 mm), their function being essentially to hold the keys 9 between them before they are broken. To effect this rupture, the usual method is to insert a spacer member into the channel 3, the assembly rod then keeping the keys uncoupled. A problem encountered with jaws of this type is that one has no control over the breaking of the bridges. The bottom of the slot 6 is flat, so that the rupture of the trigger guard can take place at practically any point along the thickness of the slot (direction perpendicular to the radial plane). The break can be zigzag because of the transverse ridges 4 formed by tapping on the wall of the cylindrical channel 3. In addition,

  trigger guard 7 often breaks in several places.

  These problems can affect the quality of the anchor. If a piece of trigger guard remains on the radial face of a key at certain points only along the length of the jaw, it may result, due to the imperfect support -3- between adjacent keys, a deformation of the

  cylindrical channel which affects the regularity of the tightening.

  Pieces of the trigger guard can still deform or separate from the key under the effect of the stresses exerted when the anchoring is carried out, these pieces then being capable of interposing undesirably between the keys, between the keys and the cable strand or between the keys and the orifice

frustoconical of the retaining block.

  It should be noted that, to tighten the strand evenly, its cylindrical channel is given a diameter

  slightly lower than that of the cable strand to be anchored.

  Thus, after a certain penetration of the streaks of the jaw in the metal of the strand and a slight radial contraction of the strand under the effect of the clamping stress, the channel regains approximately its cylindrical shape so that the stress is transmitted uniformly over the

perimeter of the strand.

  The sawn timber made between the keys leaves between them the intervals necessary for the transmission of the tightening force. In the absence of these intervals, the radial tightening exerted at the frustoconical interface would result in a tightening of the keys one on the other at the level of the radial planes, rather

  only by transmitting the tightening to the strand.

  It is advisable to avoid that when carrying out the anchoring some of these intervals are reduced while others widen. Indeed, this would result, in the worst case for a jaw with N keys, by the removal of N-1 from the intervals and by the formation of an interval of thickness N times greater. This would also cause ineffective tightening of the strand, which could cause slippage. In the typical case where N = 3 and where the cutouts leave 1.5 mm intervals between the keys, we can end up with a 4.5 mm interval which strongly disrupts the anchoring -4- of a conventional strand to seven sons whose sons

  devices have a diameter of 5 mm.

  The fact of poorly mastering the breaks of the bridges does not eliminate this drawback of traditional jaws. An object of the present invention is to improve the jaws of the type described in French patent 2,586,076

  limiting the incidence of the problems mentioned above

  above. The invention thus provides a single piece for producing a cable anchoring jaw, comprising several angular sectors arranged around a generally cylindrical channel, joined by bridges adjacent to said channel, each bridge being located at the bottom a respective radial slot extending between two of the sectors from the periphery of the part. According to the invention, each trigger guard has a surface towards its respective slot of which at least part is inclined relative to the direction perpendicular to the radial plane of said slot, so that the radial thickness of said trigger guard has a minimum in one position.

  determined according to said direction.

  When splitting the monobloc piece to obtain the keys corresponding to the angular sectors, the bridges are preferably broken at the place where their thickness has a minimum, that is to say at a place that can be controlled using a cutting

  suitable for forming radial slots in the room.

  This results in a better distribution of the clamping forces on the periphery of the part through the

  internal clamping surface at the trigger guard.

  The edges that the broken bridges leave on the radial faces of the keys at the edge of the jaw's cylindrical channel have a well-defined shape, and they can

  participate in the transmission of forces to the cable strand.

  By thus using the entire width of the angular sector, the distribution of the forces is also improved (the

peak pressures are decreased).

  In addition, these flanges practically eliminate the aforementioned problems of excessive widening of one of the intervals between keys. In an advantageous embodiment, the surface which each trigger guard presents towards its respective slot is substantially V-shaped. The inclination of the faces of the V then makes it possible to transfer the clamping forces over the entire surface of the grooves generally present on the wall of the cylindrical channel, so as to significantly increase the regularity of the tightening on each of the wires constituting the anchored strand or strand. The inclination of the faces of the V also allows the key sectors to be placed in a regularly spaced manner by the normal radial sliding of the key sector on the parts of the V. According to another aspect, the invention provides a manufacturing process a cable anchoring jaw formed by an assembly of a number N of keys, in which: a channel of generally cylindrical shape is formed in a single piece; N cuts are made in the one-piece piece from its periphery along radial planes, to form N radial slots delimiting N angular sectors of the piece, at least N-1 cuts being interrupted before reaching the channel in order to leave the bottom remaining corresponding slots of the bridges joining the sectors; - The part thus obtained is subjected to a hardening treatment; and - the N sectors are forced apart to break the bridges, each key of the jaw being

  obtained from one of the sectors.

  The interrupted cuts are made so as to give each bridge a surface, directed towards the corresponding slot, at least part of which is inclined relative to the direction perpendicular to the radial plane of said slot, so that said bridge is broken in a determined position in said direction. Other special features and advantages of this

  invention will appear in the description below

  of nonlimiting exemplary embodiments, with reference to the appended drawings, in which: - Figure 1, previously commented on, is an end view of a blank part of an anchoring jaw according to French patent 2 586,076; - Figure 2 is a perspective diagram of an anchoring jaw made in accordance with the present invention; - Figure 3 is an end view of a part

  of a jaw of the type of FIG. 2.

  FIG. 2 shows the form of an anchoring jaw 10 according to the invention, used to block a cable strand 8 such as for example a prestressing strand or even a guy strand. This example of jaw 10 has a generally frustoconical shape, with a cylindrical central bore 5, intended to be traversed by the strand 8, the internal wall of which comprises transverse ridges 11 to grip the strand well. This frustoconical shape is divided into three sectors of 120 degrees formed by three identical keys 12. These keys 12 are assembled using an annual ring 13 housed in a circumferential groove 14 near the most extreme

wide of the bit.

  This jaw 10 engages in a complementary frustoconical orifice 15 provided in an anchoring block 16. To anchor a strand, the procedure is as follows: the strand 8 is threaded through the orifice; the jaw 10 is placed around this strand; traction is exerted on the strand in its part projecting from the outer face 17 of the anchoring block 16, for example using a jack; and the jaw 10 is pressed around the strand into the frustoconical orifice 15. After loosening of the tensile force, the jaw 10 firmly blocks the strand

8 in block 16.

  As shown in Figure 2, the strand 8 can be

  consisting of seven metallic wires 7 twisted together.

  To produce such a jaw 10, one starts in a manner known per se from a one-piece part delimited externally by a frustoconical surface. In this

  frustoconical part, an axial cylindrical channel 5 is drilled.

  FIG. 3 shows such a part 20.

  The internal surface of the channel 5 is striated transversely, for example according to a helical thread with a triangular section formed by tapping, which will produce the ridges 11 on the internal faces of the keys 12. The annular groove 14, not visible in FIG. 3 is machined on the frustoconical face of the part 20 in the vicinity of its

great base.

  The part 20 in question is advantageously made of a mild steel which can easily be machined but which can be hardened superficially by a

  heat treatment such as case hardening.

  It is in this part 20 that the radial slots 25 are extended by sawing, extending along planes passing through the axis of the part and delimiting the sectors.

  angular 22 which will constitute the keys 12 of the jaw.

  In the illustrated embodiment, the number N of slots 25 is three, so that they are spaced

  angularly 120 around the axis of the channel.

  The thickness of these slots, determined by that of the cutting tool 30 used to make them, is for example 1.5 mm. The slots 25 do not pass through the material of the part 20 to the channel 5: each of them is interrupted so as to leave a bridge 27 on the

along channel 5 a trigger guard 27.

  As shown in FIG. 3, the bottom of each slot 25 is V-shaped pointing towards the axis of the part 20, that is to say towards the channel 5. To achieve this, the cutting tool used , such as a circular milling cutter or saw 30, has teeth 31 with a substantially V-shaped profile on its active edge perpendicular to the cutting plane, that is to say teeth 31 whose point shape is complementary to the desired V shape of the bottom of the slot 25. The V shape of the bottom of the slot 25 makes it possible to control where the trigger 27 will break when the pins 12 are separated. The trigger 27 will break

  preferably at the tip of the V, that is

  say approximately in the middle of the thickness of the

slot 25.

  In another embodiment, the bottom of the slot 25 could have a tapered shape other than a V-shaped profile. What is important is that this shape is such that at least part of the surface of the trigger guard facing the slot is inclined relative to the direction X perpendicular to the radial plane of said slot, so that the radial thickness of said trigger guard has a minimum at a position determined in this direction X.

  It is at this minimum that the rupture will take place.

  The advantage of the V shape is its ease of construction. By way of example, it can be provided that the thickness of the trigger guard, measured between the tip of the V and the wall of the channel 5, is between 0.8 mm (at the bottom of the ridges 11) and 1.3 mm (at the level of the top of the ridges 11), the angle a between the two inclined faces of the V being by

example of 90.

  It should be noted that, despite the fineness of the thickness and the shape of the slot 25, it is relatively easy to adjust the sawing accordingly since the three slots can be performed simultaneously using three thin tools, the respective dimensions and positions are rigorously determined and between which the

part 20 is forced axially.

  The jaw blank thus cut remains in one piece and can be mixed in bulk with

other similar pieces.

  The stresses exerted on the bridges 27 at this stage are indeed much lower than those which would be necessary to break them. The bridges have not yet been weakened by case hardening and therefore essentially have the function of maintaining a connection

  between the sectors 22 corresponding to the keys 12.

  We then take one by one the one-piece parts 20 which are not yet divided into separate keys, so as to place the assembly rod 13 in each

  groove 14, rod generally made of spring steel.

  The whole is then subjected to the case hardening treatment which leads to the surface hardening of the

keys 12 and bridges 27.

  This treatment can be a heating at a temperature between 900 and 1000 C, carried out for three quarters of an hour in a fuel atmosphere,

heating followed by quenching.

  The steel thus treated then became superficially very hard, and the bridges 27 became

relatively fragile and brittle.

  The simple grip of the assembly at this stage may be sufficient to break the bridges 7. Otherwise, there is a spacer member at the mouth of the channel 5, and the bridges are broken by striking this member. The keys 12 of the jaw are then separated from one another, in

remaining attached by the rod 13.

  As shown in Figure 2, the broken bridges leave on the radial faces of each key edges 28 of approximately triangular section. These flanges 28 are adjacent to the channel 5 in which the jaw clamps the strand 8. They thus participate in the transmission of the tightening forces to the strand, preventing the tightening force of the strand from decreasing over too wide an interval

- 10 -

  between the keys. Correlatively, the peak pressures

  the strands are reduced.

  The flanges 28 also prevent that during the realization of the anchoring, some of the intervals between keys have a tendency to narrow, causing

  widening of another interval.

  A number of variants can be made to the embodiment described without departing from the scope of the present invention, for example: - the number N of keys could be different from three; - the periphery of the jaw may not be simply frustoconical; it could be composed of several successive frustoconical sections or even be curved; - one of the N cuts made in part 20 could be complete, the part remaining in one piece with only N-1 bridges; - the order of execution of certain process steps

  manufacturing method of the anchor jaw could be modified.

- he -

Claims (7)

R E V E N D I C A T I ON S   1. Monobloc piece (20) for producing a cable anchoring jaw (10), comprising several angular sectors (22) arranged around a generally cylindrical channel (5), joined by bridges (27) ) adjacent to said channel, each trigger guard being located at the bottom of a respective radial slot (25) extending between two of the sectors from the periphery of the part, characterized in that each trigger guard has a surface towards its respective slot, a part of which at least is inclined relative to the direction (X) perpendicular to the radial plane of said slot, so that the radial thickness of said trigger guard (27) has a minimum in a determined position in said direction (X).   2. One-piece part according to claim 1, in which the surface which each trigger guard (27) presents towards its respective slot (25) is substantially V-shaped. 3. Method for manufacturing a cable anchoring jaw (10) formed by an assembly of a number N of keys (12), in which: - a channel (5) of generally cylindrical shape is formed in a single piece; - N cuts are made in the single piece from its periphery along radial planes, to form N radial slots (25) delimiting N angular sectors (22) of the piece, at least N-1 cuts being interrupted before reaching the channel (5) in order to leave at the bottom of the corresponding slots of the bridges (27) joining the sectors; - The part (20) thus obtained is subjected to a hardening treatment; and - the N sectors are separated from each other in order to break the bridges, each key (12) of the jaw being obtained from one of the sectors (22), - 12 -   characterized in that said interrupted cuts are made so as to give each bridge (27) a surface, directed towards the corresponding slot, at least part of which is inclined relative to the direction (X) perpendicular to the radial plane of said slot , so that said trigger guard is broken in   a determined position in said direction (X).   4. The method of claim 3, wherein said N-1 cuts are made at least by means of one or more tools (30) having teeth (31) in profile.   substantially in V perpendicular to the cutting plane.   5. Method according to claim 3 or 4, wherein one taps the generally cylindrical channel (5) to form transverse ridges (11) on an inner face of each key (12).   6. Method according to any one of the claims   3 to 5, in which an annular groove (14) is formed on the periphery of the single piece (20), and an assembly ring (13) is engaged in this groove before proceeding to the hardening treatment.   7. Cable anchoring jaws (10), formed by an assembly of several keys (12), obtained by a   method according to any one of claims 3 to 6.